Minimum Viable Population

Gopher Tortoise Minimum Viable Population and Minimum Reserve Size Working Group Report

Prepared by: The Gopher Tortoise Council

10 October, 2014

The second Gopher Tortoise Minimum Viable Population and Minimum Reserve Size Workshop was held 4-5 March 2014 at the Solon Dixon Forestry Education Center in Andalusia, Alabama as a follow-up to the first workshop (Gopher Tortoise Council 2013). The consensus from the first workshop was that a minimum viable population (MVP) for the gopher tortoise is 250 adults with a density of no less than 0.4 tortoises/ha and that the minimum reserve size for a MVP to persist is 100 ha of superb habitat.

The objectives for the second workshop were to:

1) Establish consensus on the number and distribution of viable gopher tortoise

(Gopherus polyphemus) populations necessary to ensure the long-term viability of the

A workshop was held on 13-14 March 2013, to define the minimum viable population (MVP) for the gopher tortoise (Gopherus polyphemus) using the best available scientific information. In this case, the purpose of establishing MVP parameters is to provide acceptable benchmarks for conservation and recovery efforts and is not to determine absolute minimum thresholds that if not met will result in certain population demise. Invited attendees included gopher tortoise biologists, land managers, and experts in demographic modeling (Table 1).

Background The U.S. Fish and Wildlife Service’s 12-month finding for listing the gopher tortoise as Threatened under the Endangered Species Act (ESA) has stimulated additional interest in conservation of the species. A Candidate Conservation Agreement and a comprehensive conservation strategy have been developed for the gopher tortoise. It will be necessary to define a minimum viable population size, the number of viable populations needed, and the ideal geographic distribution of these populations in order to successfully conserve this species.

The scientific literature provides mixed guidance about what constitutes a minimum viable gopher tortoise population. Results from existing population viability models vary from 25 to 250 individuals under ideal habitat conditions (Table 2). In addition, there is no consistency in the scientific literature regarding how large a parcel of habitat must be to support a viable population. Therefore, there was a clear need to convene experts in gopher tortoise biology, ecology, management, and demographic modeling to reach consensus regarding the following objectives:

Define a minimum viable gopher tortoise population size based on the best scientific information available.

Identify the minimum reserve size needed to support a viable gopher tortoise population.

Identify the number and distribution of viable gopher tortoise populations necessary to ensure the long-term viability of the species.